1. Field of the Invention
The present invention relates to a plastic bumper for use in automobiles and, more particularly, to the structure of such plastic bumpers with rigid construction and capable of being formed by blow-molding.
2. Description of the Prior Art
Instead of metallic bumpers, plastic bumpers have been proposed However, the conventional plastic bumpers have thick wall structure to prevent easy deformation or destruction by external forces o impacts. Such structure results in heavyweight and high cost. Furthermore, such heavy bumpers are not easy to assemble to the automobile body, and are not contributing to produce a light weight automobile. If such plastic bumpers are made with thin plastic walls, there have been problems in the durability with respect to various external impacts.
For example, in FIG. 1, a cross-sectional view of a prior art plastic bumper formed by blow molding is shown, which is formed by a rear wall member 23 having a mid portion indented continuously along the lengthwise direction of the bumper to form a groove with a V-shape cross-section and a front wall member 22 having a U-shape cross-section. The outer bottom end face of the indented portion of the rear wall member 23 is adhered to the inside face of front wall member 22, by press welding.
Although the bumper structure shown in FIG. 1 is strong with respect to horizontal direction impacts, it is weak with respect to vertical direction impacts.